1. Field of the Invention
The present invention relates to a turn angle indicator or angular displacement indicator and, more particularly, relates to a capacitive turn angle indicator, especially a positioning sensor for a flap or throttle valve, including a supporting plate fastened to the apparatus at a close narrow distance in front of a further supporting plate which is rotatable planar-parallel relative thereto and which is utilized for a mutually oppositely located narrow spoke or sector-shaped electrode pattern, and with a bearing structure for the rotatable supporting plate and which is fastened to the apparatus.
2. Discussion of the Prior Art
An angular displacement or turn angle indicator has become known from the disclosure of German Laid-Open Patent Appln. No. 29 37 248. The rotatable shaft of the movable electrode supporting plate thereof is supported in the bottom of a cup-shaped housing, and extends freely through the stationary electrode supporting plate which is fastened to the housing and which serves as a housing cover. This shaft is turned by the component, whose momentary position is intended to be measured by means of a capacitive analysis of the degree of overlapping by the sector-shaped electrodes, in that; for instance, there is directly measured the resulting capacitance or the magnitude of an alternating current which passes this reactance. Since in any event, the capacitance which enters into the measurement also depends upon the spacing between the electrodes, and during rapid rotational movements or during bending loads acting on the shaft this is neither constant over a period of time or over the circumference of the supporting plates, then for obtaining a reduction in the influence of spacing-dependent errors, there should be selected the largest possible spacing between the electrodes. This results in inaccuracies due to lower capacitances, which can only be compensated for by electrodes which are wide in the direction of movement; in essence, through large overlapping surfaces From this, there is finally obtained the result that the capacitive turn angle indicator of the type considered herein does not allow for the attainment of a large angular resolution and at only a limited accuracy. However, on the other hand, the latter is necessary when, for instance, for the electronically supported control over the function of an internal combustion engine there should not only be determined the flap or throttle valve position (for instance, for a carburetor or fuel injection system) with regard to specified, constructively available end positions; having reference to German Patent Specification 36 40 110, but there is to be directly evaluated the movement of the throttle valve in a precise angular resolution.